Type Analysis | Description | Corrosion Resistance | Physical Properties
Heat Treatment | Workability | Typical Mechanical Properties

Type Analysis

Description

Waspaloy is a precipitation hardening, nickel-based alloy which has been used in elevated temperature applications. The alloy has been used for gas turbine engine parts which require considerable strength and corrosion resistance at temperatures up to 1600°F (871°C). Waspaloy is usually vacuum-induction plus consumable electrode remelted.

Corrosion Resistance

Waspaloy has excellent resistance to corrosion by combustion products, encountered in gas turbines and aircraft jet engines, at temperatures up to 1600°F. Intergranular oxidation occurs at temperatures above 1600°F.

Physical Properties

Specific gravity ..................................... 8.25
Density
   lb/cubic in. ......................................... 0.294
   kg/cubic meter ................................... 8138

Modulus of Elasticity

Electrical resistivity

Mean coefficient of thermal expansion

Thermal conductivity

Specific Heat

Heat Treatment

Annealing
Hardening and strength properties are developed by precipitation of gamma prime (Ni3TiAl). The solution temperature for gamma prime in Waspaloy is normally 1860/1880°F. This is also the temperature range at which grain growth begins. Annealed, or low hardness can be obtained only by cooling very rapidly from temperatures above the gamma prime solvus. Water quenching will result in hardnesses as low as Rockwell B 90, while air cooling will result in Rockwell C 28/30. Uniform low hardness cannot be obtained on sections having condiderable mass. Air cooling is desirable for large sections.

Hardening
Best stress rupture and creep properties are generally obtained by high temperature solution treatments, 1900/1975°F. The 1975°F temperature will result in coarse grain size, low tensile yield strength and low tensile ducitility. If the alloy is treated below solvus temperature at, for example, a temperature of 1825°F, the as-hot-worked grain size will be retained and high tensile yield and tensile ductility will result, with some loss in stress-rupture properties.
A practical compromise for adequate rupture properties, acceptable tensile properties and moderate grain growth is: solution treat just above the gamma prime solvus temperature, 1875/1900°F. Rotating parts are generally treated toward the low side, 1865/1875°F. For rupture-oriented applications, treating toward the high side, 1900/1925°F, is suggested.
The normal aging treatment for Waspaloy is: stabilize 1550°F 4hrs, air cool, followed by precipitation aging 1400°F, 16 hrs, air cool. However, if solution treating is 1975°F, the 1550°F stabilization aging time is increased to 24 hours, instead of the usual 4 hrs.

Workability

Hot Working
Hot working is usually conducted in the temperature range 1850/2150°F. The recommended furnace temperature is 2150°F. Finishing should be discontinued at a temperature not lower than 1850°F (optical). Whether possible, the hot working should proceed at a rate designed to maintain the proper hot-working temperature through internal "frictional heat." If deformation is too rapid, the temperature of the workpiece can "build up" and exceed the recommended 2150°F temperature and "hot short" tears will result. The alloy is normally air cooled from the hot-work operation.

Cold Working
Waspaloy has reasonably good cold ductility when annealed either above or below the gamma prime solvus temperature. Since the alloy work hardens very rapidly, frequent anneals will be required. Minor reductions, or sizing operations, should be avoided; otherwise critical strain can cause severe grain growth during subsequent solution treatments.
Cold worked areas will age more rapidly than unworked sections. Contraction during aging of worked areas will result in severe and complex stresses during heating through the aging temperature range to a solution or annealing temperature. If shallow or nonuniform cold working is unavoidable, strain-age cracking can develop unless the part can be heated extremely rapidly through the aging temperature. Thus, cold worked parts should not be aged. A nonuniformly cold-worked part should not be put into service where the operating temperature will reach the aging temperature range, probably 1000/1600°F.

Machinability
Waspaloy is difficult to machine in any condition of heat treatment. The air-cooled, solution treated condition is best for most operations (this is Rockwell C 30 partially aged). Rigid, well-powered machines are required for best results. Cemented cardide tools are preferred for most operations and care must be exercised to obtain positive cuts at all times, otherwise "glazing over" and work hardening of the surface will occur.
The following tool geometry, feeds, and speeds have been found satisfactory for lathe turning:
0° back rake
6-8° side rake
5-8° clearance (end and side)
15-20° lead angles may be used to reduce feed pressure on roughing cuts.
Speeds of 35/50 sfm with feeds of 0.005/0.15" per revolution are recommended. Slower speeds and greater feeds should be used for roughing cuts, and faster speeds and lighter feeds for finishing cuts. Better tool life will be obtained by machining in the solution treated condition; however, a smoother finish can be obtained by machining in the fully aged condition.

Welding
Waspaloy should always be in the annealed or solution treated condition before attempting welding. Good fit up and careful control of arc length and current input will minimize weld restraint. A clean surface is important--chemical descaling, cleaning solvents, vapor blasting (not sand blasting), and emery cleaning are recommended.
Any molten weld metal should be protected from atmospheric contamination. Argon is recommended for both sides of butt joints. Rapid cooling of the weld area is best practice. Copper back-up bars and /or water-cooled fixtures or sprays are recommended.
All welded parts should be re-solution treated. "Strain-age" cracking can be minimized by heating welded parts through the aging temperature as rapidly as possible.

Typical Mechanical Properties

Bar Stock
Tensile Properties

* Aging: 1550°F (843°C)/4 hours/A.C. + 1400 (760°C)/16 hrs/A.C.

Stress Rupture

* Aging: 1550°F (843°C)/4 hours/A.C + 1400 (760°C)/16 hrs/A.C.

Waspaloy - Current Inventory Stock